This invention relates to casting continuous metal strip using a segmented roll. More particularly, the invention relates using a casting roll formed from an assembly of similar annular segments having a common diameter. The segmented roll lowers the cost of producing a casting roll and allows for larger width rolls to be manufactured. The segmented casting roll may also enhance solidification of the melt to the roll outer chill surface and minimize defects on the chill surface during casting of metal strip.
Direct strip casting involves bringing a melt into contact with a liquid cooled substrate such as the chill surface of a metal casting roll, e.g., copper. This may be accomplished by casting the melt onto a single casting roll rotating past a refractory pouring nozzle or by pouring the melt into the meniscus formed between a pair of opposing rotating casting rolls, i.e., twin rolls. Intimate contact of solidifying metal to a bare metal substrate is required to achieve a high cooling rate. The casting roll includes channels, through which a cooling liquid such as water or gas is circulated, extending through the entire width of the roll. This cooling liquid carries away heat absorbed from the molten metal introduced into the interior of the roll. As the solidified metal strip cools while still in contact with the chill surface of the casting roll, the strip contracts. This contraction results in very high tensile stresses due to constraint from the chill surface. The solidification rate of the strip is determined by the heat transfer rate. Accordingly, cooling of the casting roll is of critical importance to successfully casting metal strip.
Casting rolls are one or two-piece and manufactured by machining an ingot into its final form. By its very nature, this roll manufacturing process is time consuming and expensive. The diameter and width of the rolls that can be produced are limited to the size of the ingot that can be cast. Furthermore, the machining operations that can be performed on this casting restrict what can be done in terms of consistency and shape. For example, openings and cooling channels within the roll must be straight. Any texturing of the outer chill surface of the roll must be done using a large lathe or patterned into the chill surface using an abrasive disk, grit blasting, or texturing by rolling, chemical etching or laser cutting. These mechanisms all limit the textures and patterns available for the outer surface of a strip casting roll. While the width of the roll limits the width of a metal strip that can be produced, the surface texture, roll diameter, and cooling channel shape, location and consistency all limit the thermal properties of the roll. The ability to cast certain compositions of metal is directly related to the heat transfer properties of the casting roll. Straight bored channels must maintain a constant distance from the roll surface, severely limiting the ability to control heat transfer, and therefore, product quality near the ends of the casting roll, i.e., edge of cast strip. Furthermore, straight bored channels can create certain structural integrity problems within a twin roll casting system that employs roll force to the solidifying metal pool.
It is known to provide a one-piece casting roll including longitudinally extending coolant passages machined through the entire width of the inner body of the roll. It also is known to provide a two-piece casting roll including longitudinally extending coolant passages machined into the inner surface of a sleeve mounted over the casting roll. U.S. Pat. No. 5,887,644 discloses a copper sleeve mounted to cover a stainless steel roll body. Longitudinally extending coolant passages are defined by the interior space between the inner roll body and the outer sleeve.
Nevertheless, there remains a need for a strip casting roll that is less costly to manufacture. There also remains a need for a strip casting roll that is available in a greater variety of widths and diameters. Additional needs include a strip casting roll available in a greater variety of chill surface textures and having improved heat transfer characteristics, improved maintainability and longevity of the moderated heat transfer texture, and reduced cost casting roll repairs.
A principal object of the invention is to produce a strip casting roll having any predetermined width and diameter.
Another object of the invention is to reduce the manufacturing cost for producing a strip casting roll having any predetermined width and diameter.
Another object of the invention is to increase the control and uniformity of the heat transfer rate across the width of the chill surface of a strip casting roll and thereby control the thickness profile across the width of an as-cast metal strip.
Another object of the invention is to control the edge cooling effect of a strip casting roll.
Another object of the invention is to make the heat transfer rate across the width of a strip casting roll more uniform.
Another object of the invention is to provide for asymmetric thermal and electrical conductivity of a strip casting roll in order to enhance thermal uniformity.
Another object of the invention is that it broadens the ability to use various materials and combinations of materials in the construction of a casting roll.
Another object of the invention is to improve use of electromagnetic devices, such as are used for molten metal edge containment.
Another object of the invention is the development of a casting roll with better structural integrity for twin roll casters using roll force solidification.
The invention relates to a segmented roll for casting molten metal into a continuous strip. The invention includes a casting roll assembled from a plurality of annular segments having a common diameter. Each segment includes an axially extending opening for cooling the roll with the opening positioned near an outer chill surface of the segment. The segments are axially aligned and structurally connected so that the openings form a cooling channel extending across the width of the roll for circulating a cooling fluid to extract heat from the chill surface of the casting roll.
Another feature of the invention is for each aforesaid segment to include a plurality of cooling openings.
Another feature of the invention is for the aforesaid plurality of cooling openings of each segment to be evenly spaced and forming an annular array around each segment.
Another feature of the invention is for the aforesaid roll including means for aligning adjacent segments.
Another feature of the invention is for the aforesaid alignment means to include at least one axially extending opening positioned a distance inside the array and an alignment mechanism extending through each of the alignment openings.
Another feature of the invention is for the aforesaid segments having textured outer surfaces.
Another feature of the invention is for adjacent ones of the aforesaid segments having different textured outer surfaces.
Another feature of the invention is for adjacent ones of the aforesaid segments being formed of different materials.
Another feature of the invention is for adjacent ones of the aforesaid segments having different axial thicknesses.
Another feature of the invention is for both planar surfaces of the aforesaid segments to include an insulative coating.
Another feature of the invention is for the aforesaid segments being slightly rotated relative to each other to form spiral cooling channels extending through the roll.
Another feature of the invention is for the aforesaid segments being metal.
An advantage of the invention includes a major cost savings to produce a strip casting roll having any predetermined width and diameter from a plurality of small annular metal segments having a common diameter rather than from a one-piece machined large cast section.
Another advantage of the invention includes flexibility in the internal geometric design of coolant channels thereby allowing differential cooling across the width of a strip casting roll.
Another advantage of the invention includes flexibility in the external design of the chill surface of a strip casting roll by having multiple textures and/or coatings across the width of the roll.
Another advantage of this invention is being able to form a metal casting roll that resists current flow therethrough thereby enhancing the use of an electromagnetic device for inducing magnetic force into the molten metal during casting.
Another advantage of the invention is that it may increase the uniformity of heat transfer, allowing improved surface quality of cast metal strip, improved strip thickness uniformity and less surface wear to the casting roll.
Another advantage includes cost savings resulting from being able to use smaller manufacturing equipment, higher production speeds, and less scrap when manufacturing the casting roll.
Another advantage of the invention is the possible use of a clamping mechanism to hold the segments in place resulting in less distortion of the casting roll due to thermal expansion characteristics. This also would allow removing damaged segments as well as the ability to change cast width diameter without having to maintain a large inventory of casting roll sizes.
The above and other objects, features and advantages of the invention will become apparent upon consideration of the detailed description and appended drawings.